Electronic high frequency dual electron beam return wave tube with cycloid beam



May 21, 1963 R. MULLER 3,090,835

ELECTRONIC HIGH FREQUENCY DUAL ELECTRON BEAM RETURN WAVE TUBE WITHCYCLOID BEAM Original Filed Nov. 25 1957 3 Sheets-Sheet 1 Fig.1

(negative energy transport) slow space charge Wave (negative energytransport) C/pn c/ vom fast space charge wave (positive energytranspori) \(n egative energy transporl) (positive energy transport) fim/rgfor May 21, 1963 R. MULLER 3,090,885

ELECTRONIC HIGH FREQUENCY DUAL ELECTRON BEAM RETURN WAVE TUBE WITHCYCLOID BEAM Original Filed Nov. 25, 1957 3 SheetsSheet 2 Fig.2

(negative energy t ranspori) (positiveenergy transport) (positive energytransport) (negative energy transport) J;ZZ/6i@ 07 May 21, 1963 R MULLER3,090,885

ELECTRONIC HIGH FREQUENCY DUAL ELECTRON BEAM RETURN WAVE; TUBE WITHCYCLOID BEAM Original Filed Nov. 25, 1957 3 Sheets-Sheet 5 3,99%,885Patented May 21, 1963 ice ELECTRONIC HIGH FREQUENCY DUAL ELEC- TRQN BEAMRETURN WAVE TUBE WITH CY- CLGID BEAM Rudolf Miiller, Strasslach,Germany, assignor to Siemens & Halske Aktiengesellschaf Berlin andMunich, a corporation of Germany Griginal application Nov. 25, E57, Ser.No. 698,576. Di-

vided and this appiication Get. 5, 1959, Ser. No. 844,562 Claimspriority, application Germany Dec. 7, H56

6 Claims. ((31. 315-3.6)

This invention is concerned with a twin electron beam return-wave tubecomprising a decoupling system for the high frequency energy and afocusing system for bundled conduction of the electron beams. Thisapplication is a division of copending application Serial No. 698,576,filed November 25, 1957, now abandoned.

The theory of the coupled wave has been developed in order to comprehendin a common point of view the physical phenomena taking place inpropagation field tubes referred to respectively as traveling fieldtubes and traveling wave tubes and return-wave tubes. For this purpose,the individual structural elements of the tubes, the line and theelectron beam, are separately investigated, that is, the so called freewaves are determined. The reciprocal action between the beam and theline is thereafter observed by the introduction of a coupling which iseffective along the entire discharge path, thus obtaining as theresultant the coupled wave. The advantage of this approach is, that thestructural elements are individually investigated, thus making itpossible to determine their properties or characteristics in advance.The tube can then be constructed in accordance with the building blockprinciple, by combining the properties of the individual structuralelements. It is in this manner possible to provide for operatingconditions as, for example, self-excitation or amplification, by thecombination of the properties of the structural elements.

As is known from the theory of the delay line, the phase velocity of a(partialor sub-) wave may have a direction corresponding to that of thegroup velocity or a direction opposite thereto. Waves with identicaldirection of the phaseand group velocity are referred to as forwardwaves and waves with opposite phaseand group velocity are referred to asreturn waves.

if the delay line with periodic structure is substituted by an electronbeam having properties corresponding to those of the delay line, theelectron beam may be considered in the nature of a moving delay line.

The electron beam has in its unmodulated condition a kinetic energywhich is determined by the velocity and the number of electrons passingthrough a cross-sectional area. If the electron beam is excited in acontrol path, there will be produced two space charge waves. The artdistinguishes thereby between slow and fast space charge waves. The fastspace charge wave effects accumulation of the fast electrons andconsequently an increase of the energy passing the correspondingcross-section, this behavior being referred to as positive energytransport. The slow space charge wave effects accumulation of the slowelectrons, therewith decrease of the energy passing the cross-section,the corresponding behavior being referred to as negative energytransport.

The above explained two possibilities concerning the energy transport,and the distinctions between forward and return waves, result in fourgroups of properties (waves) with respect to the individual structuralelements of ultra high frequency tubes, namely, 1) forward waves withpositive energy transport; (2) return Waves with positive energytransport; (3) forward waves with negative energy transport; and (4)return waves with negative energy transport.

Waves of the groups (1) and (2) are the known partial or subwaves alonglines. The free space charges in a homogeneous electron beam are for themost part waves of the groups (1) and (3). (A wave of the group (1)becomes a wave of the group (2) only in the case of low frequencies.)

In case of a diffusing field, as is present with delay lines of periodicstructures, there will be several partial waves which have a commongroup velocity. The energy transport is defined only for the entirety ofall partial waves. The entirety or totality of all partial waves affectsthe electrons of the electron beam. The effect of the non-synchronouspartial waves may be neglected only over lengths which are great ascompared with the cycle of the line structure. The arrangements andmodes of operations according to the invention apply, accordingly, onlyto lengths which are very much greater than a cycle of the periodicstructure.

Several kinds of arrangements and modes of operation for theamplification and generation of ultra high frequencies are possiblebased upon combinations of the four previously mentioned groups.

The combination of the group (1) with group (3) will result in anamplifier operating according to the principle of the known travelingfield tube. The wave of the group (l)-forward wave upon a delay linewith periodic energy transport-is coupled with wave of group (3)--for-Ward wave in the electron beam, with negative energy transport. Thecombination of the group (2) with the group (3) results in the knownreturn-wave tube which is likewise based upon the principle ofpropagating field tubes with delay lines. In such case, a forward wavewith negative energy transport is coupled with a return wave withpositive energy transport.

These known ultra high frequency tubes, which are used for amplificationas well as for the generation of ultra high frequencies, comprise as astructural element a delay line which is operative to delay theelectromagnetic wave with respect to its diffusion velocity, so as tomatch its velocity to that of the electron beam. Delay lines have thedrawback that the electric field, required for the coupling of theelectron beam, decreases exponentially with the distance from the delayline. The electron beam must for this reason he guided very close to thedelay line. Heating of the delay line by electron bombardment is,accordingly, unavoidable and, in addition, cumbersome focusing devicesare required for the bundling of the electron beam. 7

Electron beam tubes for the amplification of ultra high frequencies arealso known, wherein two electron beams extend mutually parallel inidentical direction, reciprocally affecting one another. The structureaccordingly constitutes a type of traveling field tube operat ingaccording to a combination of groups (1) and (3). The drawback of suchtube is, that its efiiciency is low zl s compared with traveling fieldtubes comprising delay mes.

The object of the invention is to eliminate the above describeddrawbacks by the provision of tubes for generating ultra highfrequencies, operating without delay lines, and simplifying, if notentirely eliminating, the costly expenditures for extensive magneticfocusing devices for the bundling of the electron beam.

The essential feature of the return wave tube with two electron beamsand an uncoupling system for ultra high frequency energy and focusingsystems for bundling the electron beams resides therein, that the twoelectron beams are propagated in opposite directions, and that they areperiodically in reciprocal interaction such, that a forward Wave withpositive energy transport of one electron beam is coupled with a returnwave with negative energy transport of the other electron beam(combination of groups (1) and (4)) or, that a return wave with positiveenergy transport of one electron beam is coupled with a forward wavewith negative energy transport of the other electron beam (combinationof the groups (2) and (3)).

If an electron beam exhibits along a given coordinate a periodicstructure, for example, periodic acceleration and delay or periodiccross-sectional alterations, it will be impossible to explain thebehavior of the beam merely by the two space charge waves; a multitudeof partial waves of identical frequency and different phase velocitywill be obtained for each of the two space charge waves. This phenomenonof splitting or subdividing into partial waves is similar as in the caseof delay lines with periodic structure, with the difference, that, inthe case of electron beams with periodic structure, the partial waveswill be allotted to the space charge Waves. All partial waves associatedwith the slow space charge wave transport negative energy; all partialwaves associated with the fast space charge wave, transport positiveenergy. Waves of all four groups are thus obtained, but of these waves,only that of the group (4) can be generated by a periodic electron beam.However, the periodic electron beam can also generate waves of the group(3).

As'has been said before, in the case of space charge waves in theelectron beam, a distinction is made between a fast and a slow spacecharge wave. From this distinction flows the manner of recognizing thepositive and negative energy transport. If one group of the previouslynoted combinations is allotted to one electron beam and another group tothe other electron beam, care must be taken to achieve the reciprocalaction between both electron beams by suitable coupling of the Wavesthat are present therewith. This coupling is only made possible (as willbe apparent from the dispersion diagram to be presently discussed) bycoupling one partial Wave of the electron beam which transports negativeenerg with the wave of the other electron beam. Accordingly, there mustobtain a periodicity which generates the partial wave, to make thiscoupling possible.

i The foregoing considerations indicate that there are several ways torealize the invention. Some of the possible embodiments shall now bedescribed with reference to the accompanying drawings, showing examplesof embodiments in simplified partially schematic representation. Alldetails not absolutely necessary for an understanding of the invention,for example, focusing systems, vacuum vessels, uncoupling devices, etc.,have been omitted from the drawings.

7 FIG. 1 is a dispersion diagram showing the partial waves contained inthe electron beam;

FIG. 2 repeats the dispersion diagram of FIG. 1, showing in addition thedispersion curves of waves of a second electron beam;

FIG. 3 indicates an example of an embodiment for efiecting theoperations according to FIG. 2; and

FIG. 4 represents an embodiment wherein one electron beam is propagatedas a cycloid while the other beam is propagated as a homogeneous beam.

Referring now to FIG. 1, a distinction is made between partial waves n+1; 1; +2; 2; etc.) belonging to the slow space charge wave (negativeenergy transport) and to the fast space charge wave (positive energytransport), respectively. The dispersion curve of the slow space chargewave is indicated by dot-dash lines, and the dispersion curve of thefast space charge wave is indicated in full lines. vacuum, and theordinate plots the ratio (c/pn) of the speed of light to phase velocity.Reference c/vom represents the ratio of the speed of light to averageelectron velocity of the unmodulated electron beam. The ratio Theabscissa plots the wave length 1 inv 4 of speed of light to phasevelocity is determined by the equation:

L L A .h pn v0m R L wherein c speed of light;

pn=phase velocity of the nth partial wave; vom average electronvelocity; k vacuum-wave length;

X =average plasma wave length; and L=length of the spatial cycle.

The plus or minus symbol preceding A /x will designate the presence ofnegative or positive en ergy transport, respectively. The factor n,preceding M/ L expresses the partial wave that is to be considered.

It will be seen from FIG. 1, that the waves n=0 have only slightdispersion. The partial waves for n= l have great dispersion andintersect the abscissa. These partial Waves above the abscissa areforward waves, and those below the abscissa are return waves. FIG. 1shows merely the dispersion diagram for one electron beam with spacecharge waves, in a-case when partial waves are produced by a periodicityaifecting the corresponding electron beam or contained therein,respectively.

FIG. 2 again shows the dispersion diagram according to FIG. 1 and inaddition thereto, underneath the abscissa, the waves of a secondelectron beam having a direction of propagation which is opposite tothat of the first beam. The partial waves (n=l) of the electron beamare, underneath the abscissa-intersecting points a and b return waveswhich intersect the forward waves (21:0) of the electron beam at thepoints 1 and 2. (FIG. 2). At point 1, there will result the combinationof groups (1) and (4), and at point 2, there will result the combinationof the groups (2) and (3). The conditions for self-excitation arepresent in both combinations and there will, therefore, result a returnwave generator.

The physical operation is essentially based upon the manner in which oneelectron beam affects .or influences the other electron beam. Thecoupling is effected over partial waves depending upon the electronvelocities and the cycle length. Accordingly, when one electron beam isaffected by electrons of the other electron beam, such influence istransported due to the electron velocity of the first beam, thusaffecting again the other electron beam. It will, therefore, be apparentthat one electron beam must have :a forward Wave with positive energytransport and that the other electron beam must have a return Wave withnegative energy transport. It will likewise be apparent that, to obtainthe same mutual influencing, one of the electron beams may have a returnwave with positive energy transport and the other electron beam may havea forward wave with negative energy transport. The particular action ofthe arrangement according to the invention is primarily achieved by thepropagation of two electron beams, which are carriers of space chargewaves, in opposite directions.

FIG. 3 shows an embodiment for obtaining with simple means the mutualperiodicity of two oppositely propagated electron beams 12 and 13 whichare produced by respective electron guns 10 and 11. The direction ofpropagation of the electron beams 12 and 13 to respective collectors 29and 21 is indicated by arrows 12 and 13. The electron beams arepropagated in cycloid courses. The periodic approach of the electronbeams is effected with the large arcs of the cycloids. The length L of aperiod or cycle extends from closest approach to closest approach. Thecycloid courses of the electron beams 12 and 13 are produced jointly bystatic electric fields E2 and E1 in connection with a static magneticfield H extending perpendicular as indicated at '14. In order to producethe two electrostatic fields E1 and E2, thereare provided along thesides of the electron beams 12 and 13,

conductive layers in the form of plates 15 and 16, extending over theentire discharge length. Furthermore, there is provided a grid 17,between the electron beams, extending in parallel with and between theplates 15 and 16 and lying on a potential which exceeds the potentialconnected to the plates 15 and 16.

The periodic approach of the electron beams 12 and 13 may also beeflfected with respect to the cycloid loops by differently polarizingthe magnetic field.

The arrangement shown in FIG 3 may be modified, for example, by formingthe electron beam 13 as a homogeneous beam and the electron beam 12 as aperiodic cycloid beam, or vice versa. A corresponding arrangement isshown in FIG. 4, wherein the electron beam .12 is propagated from thegun 10' in the direction 12' toward the collector 20, just as in FIG. 3,while the beam 18 is propagated from the gun 11' in the direction 18' tothe collector 21' as a homogeneous beam. The deflection device for thecycloid course must thereby be omitted on the side of the homogeneouselectron beam.

It will be apparent from the foregoing explanations that there occurs amutual influencing of the electron beams at the points of approach, suchinfluencing always continning in opposite direction with respect to theelectron beams and causing renewed influencing at the next successivepoint of approach.

As will be seen from FIG. 2, the partial wave (21:0) is always coupledwith a partial wave (11: This coupling is made possible by dimensioningthe period or cycle length L and the electron beam velocity (vom) so,that one partial wave (n=1) of one electron beam is coupled with thepartial wave (11 of the other electron beam. It is, however, alsopossible to dimension the period or cycle length L and the electronvelocity (vom) so, that a partial wave (n=1, '2, 3 of one electron beamis coupled with a partial wave (n=l, 2, 3 of the other electron beam.Coupling of a partial wave (n=()) with another partial wave (11 :0) isunfavorable because, as is apparent from FIG. -2, the point ofintersection or crossing occurs at great wave lengths and the structurewould accordingly become too long.

The embodiment illustrated in FIG. 3 provides the great advantage ofeliminating delay lines, especially those with finest periodicstructures and, due to the oppo itely directed propagation directions ofthe electron beams, a period or cycle length for very short waves,particularly millimeter waves, which is, as compared with previouslyknown ultra high frequency tubes with delay lines, about twice as great.Accordingly, structures for ultra short waves will not require elementsdemanding high mechanical precision. For the decoupling of the generatedelectromagnetic waves, there may be used devices such as they areemployed primarily in klystrons, wherein an electrical double layer ispermeated by a density-modulated electron beam and wherein the doublelayer is connected with cavity resonators. Other decoupling devices,such as they are employed in connection with traveling field tubes, maylikewise be used when it is desired to obtain greater band width of thereturn wave tubes.

Changes may be made Within the scope and spirit of the appended claimswhich define what is belived to be new and desired to have protected byLetters Patent.

I claim:

1. A twin electron beam return wave tube, comprising means forming adecoupling system for the high frequency energy and a focusing systemfor the focused guidance of the electron beams in a single plane, saidelectron beams being propagated in opposite directions and periodicallyentering into mutually reciprocal action, said system comprising meansfor propagating said beams in mutually crossing static magnetic andelectric fields which are directed transverse to the dischargedirection, at least one of said electron beams being a cycloid beam.

2. A twin electron beam tube according to claim 1, wherein said systemcomprises means for propagating both of said beams as cycloids.

3. A twin electron beam tube according to claim 2, wherein said electronbeams are periodically moved toward each other along portions of thelarge cycloid arcs.

4. A twin electron beam tube according to claim 3, wherein the cycloidpaths of said electron beams are produced by means forming a staticmagnetic field directed perpendicularly to the beam plane thereof and bymeans forming at least one electrostatic field which is directed in thebeam plane perpendicularly to the discharge direction.

5. A twin electron beam tube according to claim 3, including a devicefor producing oppositely directed electrostatic fields, said devicecomprising a metallic sheet positioned respectively alongside eachelectron beam and extending substantially for the length of thedischarge path, said metallic sheets being respectively directedperpendicularly to the respective electron beam plane, and means forminga grid disposed between said electron beams and extending in parallelwith said metallic sheets.

6. A twin electron beam return wave tube according to claim 1, whereinone of said electron beams is propagated as a homogeneous beam while theother beam is propagated as a cycloid beam.

References Cited in the file of this patent UNITED STATES PATENTS2,684,453 Hansell July 20, 1954 2,794,146 Warnecke et a1 May 28, 19572,857,548 Kompfner et al Oct. 21, 1958 2,899,597 Kompfner Aug. 11, 19592,9 ,556 Charles et al Nov. 3, 1959 2,926,281 Ashkin Feb. 23, 1960FOREIGN PATENTS 1,106,301 France July 20, 1955

1. A TWIN ELECTRON BEAM RETURN WAVE TUBE, COMPRISING MEANS FORMING ADECOUPLING SYSTEM FOR THE HIGH FREQUENCY ENERGY AND A FOCUSING SYSTEMFOR THE FOCUSED GUIDANCE OF THE ELECTRON BEAMS IN A SINGLE PLANE, SAIDELECTRON BEAMS BEING PROPAGATED IN OPPOSITE DIRECTIONS AND PERIODICALLYENTERING INTO MUTUALLY RECIPROCAL ACTION, SAID SYSTEM COMPRISING MEANSFOR PROPAGATING SAID BEAMS IN MUTUALLY CROSSING STATIC MAGNETIC ANDELECTRIC FIELDS WHICH ARE DIRECTED TRANSVERSE TO THE DISCHARGEDIRECTION, AT LEAST ONE OF SAID ELECTRON BEAMS BEING A CYCLOID BEAM.